1. Field of Invention
The present invention relates to high-powered light emitting diodes, more particularly to improving the thermal properties of high-powered light emitting diodes with flip-chip architecture.
2. Description of Related Art
Light emitting diodes (“LEDs”) are solid-state light sources with multiple advantages. They are capable of providing light with high brightness reliably and thus find applications in displays, traffic lights, and indicators, among others. An important class of light emitting diodes is fabricated from one or more Group III elements, such as gallium, indium, or aluminum, and the group V element of nitrogen. These “III-nitride” LEDs are capable of emitting light in the green, blue, or even ultraviolet regime of the spectrum, and thus have many promising applications. Other suitable materials systems for fabrication of light emitting diodes include the III-phosphide, III-arsenide and II-VI materials systems.
LEDs are often fabricated by epitaxially depositing an n-type region, an active region and a p-type region on a substrate. Contacts, typically metal, are formed on the n-type region and the p-type region. During operation, the contacts provide current to the n- and p-sides of the device. In some types of devices, for example III-arsenide devices, the growth substrate is often removed after growth, an n-contact is deposited on the exposed n-type region, and a p-contact is deposited on the p-type region. In other types of devices, a portion of the active region and the p-type region are etched away, exposing a portion of the n-type region. The p-contact is formed on the remaining portion of the p-type region and the n-contact is formed on the exposed portion of the n-type region, such that both contacts are formed on the same side of the device. In such a device, the light may be extracted from the device through the contacts or through the side of the device without the contacts. Devices that extract light through the contacts are generally disfavored because in order to provide enough current to the device, the typically metal contacts must be thick enough that they are essentially opaque. Devices that extract light through the side of the device without the contacts are referred to as flip chips. III-nitride devices are often grown on sapphire substrates and included in devices in flip chip configuration.
In general, as the amount of current provided to the device increases, more electrons and more holes are provided to the active region, resulting in more photons being emitted. In III-nitride devices however, as the current density increases, eventually efficiency decreases, then failure mechanisms such as cracking of the sapphire substrate or the device layers are observed.